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Unread 09-06-2005, 00:09
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Re: Chemistry Question

Alright, I guess I'll make an example.

In the system of acetic acid (HC2H3O2<----> H+ + C2H3O2-), Ka=1.8x10-5. If [HC2H3O2] = [H+] = [C2H3O2-] = 1.0 M

a. Find Q
b. Predict which direction the reaction will shift in order to reach equilibrium

a. First, write the Ka expression, which will be
[H+][C2H3O2-]
[HC2H3O2]

The expression will be the same as the Ka expression. So Q also equals
[H+][C2H3O2-]
[HC2H3O2]

Plug in the values for concentrations given. This gives you (1x1)/1.

Q=1

b. Since Q>Ka, the amount of products is too high (you can think of this as having to make Q smaller until it reaches Ka). Therefore, the reaction needs to shift to the reverse reaction until Q=Ka


The same thing can be done with Kc and Kp in gaseous systems.

Does this help?
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